This invention relates to a fire protection system, and more particularly to a fire protection system which includes an automatic self-test circuit. The circuit has particular utility with fire control systems of the type used in, for example, textile mills or other industrial environments where flammable materials such as textile fibers are entrained in a moving air stream and thus conveyed at high speed through enclosed duct work. Typically, the fibers are moved between processing stations. Infrared detectors are positioned in the duct work at intervals and are designed to detect the presence of embers or hot metal fragments in the moving air stream which could cause a fire or explosion. An infrared detector detecting a source of infrared energy in the moving air stream sends a signal to a control panel, where signals are transmitted to instantly shut off the fiber processing equipment. Signals may also operate diverters, fire extinguishers or other equipment intended to protect life and property from a fire or explosion.
Fire control systems are required to be inspected periodically to ensure that the system and its components are working properly. This periodic inspection is time consuming and labor intensive, therefore leading to the possibility that the inspection is not performed as diligently as it should be, or is not performed at all.
By automating this process, and causing it to be initiated automatically at a predetermined time each day, each week, or each month, a complete inspection can be performed to test each detector, and any detector failing the test will cause the system to show a trouble indication. The failed detector must be corrected before the system will clear the trouble indication. A record of each test is kept by the system for use of the authority having jurisdiction.
The major function which must be performed in order to fully implement the self-test feature is the ability to accurately ascertain which of the infrared detectors has been activated so that those which fail to activate may be reported. There have been a number of systems implemented that use serial communications as a means to provide detector address information. These have ranged from using a shared packet bus, as in the commercially available "Mastermind" panel, to the use of more powerful packet systems such as the commercially available "LonWorks" protocol. Each of these has carried a high cost of the interface and required additional wiring to the detector to carry this address information.
This application discloses a system wherein the address information is shared with the standard annunciator information brought back from the detector. This reduces the cost to implement and eliminates the need for either additional and/or more costly wiring to the detectors. Thus, the annunciator capability of the individual detectors transfers the information to the individual zone control of the control panel, identifying exactly which detector has sensed a fire, or in the case of testing, which detectors, if any, failed the detector test.
This application disclosed two implementations of the invention. Both implementations use a low cost microcontroller to act as the interface of the detector to the media both at the detector as well as the zone card. At the detector end, the microcontroller supervises the annunciator output from the detector which goes from a 0V state to a 24VDC state whenever a fire is detected. The microcontroller is attached to the media formerly used to carry the annunciator signal back to the zone card. It is attached so that one output may drive the media and one input monitors the state of the media. These I/O pins are attached such that the annunciator line becomes a shared bus for all of the detectors in the zone. The coupling is such that any detector may drive the bus high at any time except when the zone controller is driving the bus low.
In the first implementation, the detector interface accepts the annunciator input for the detector and drives the bus from a quiescent state of low (0V) to a high state (+5V). This change of state is detected by the microcontroller located on the zone card. Once the zone card has posted the event, the zone card drives the bus low to indicate to the detectors that have detected a fire they should send back their addresses. When the bus is pulled low by the zone card, all detectors that have detected a fire change their bus drives from a high to a low. After a short period of time, for example, 10 ms, the zone card drives the bus high briefly to indicate the state of a query frame. The query frame is a set timeslot, each having a period of 4 ms.
Each detector in the zone has a unique address ranging from 1 to 128. During the query frame, each detector will drive the bus high during the timeslot that is mapped to the detector's physical address. For example, if detector 5 has detected a fire, then it will pulse its output high during the 5th, 4 ms timeslot. Both the zone controller and the individual detectors keep track of the timeslots by internal timers in each controller that counts the timeslot in use after the start of query frame transition. The zone controller senses these high states from the detectors and logs those timeslots that have the bus high as having a detector with a fire indication. The total query time is 128.times.4 ms, or about 0.5 seconds.
This process is ideal where the microcontroller's oscillators are driven by some accurate method such as with a crystal. This accuracy is required since all processors are counting from the same start of frame edge and for 128 addresses the combined error of any two oscillators would have to be less than 1/128, or the timeslots may be corrupted.
The second implementation further reduces the expense and complexity of the system by using internal RC oscillators that are present in very low cost microcontrollers. Thus, the need for accurate measurement as described above is eliminated. This is achieved by eliminating the need for a processor to count from the single start of frame. Instead, the zone controller synchronously clocks the timeslots onto the bus. The zone controller is therefore modified to create the start of frame as before. However, rather than simply driving a single start of frame pulse, the zone controller now drives the bus 128 times at a 4 ms interval with each high transition lasting 2 ms. Each of the positive transitions now indicates a timeslot and then during the low state condition, any detector with a fire indicated will pulse the bus high to indicate that there is a fire. This implementation allows each processor to reset its timer and re-synchronize with the zone, thus allowing for very low accuracy clocks to be used.
The second implementation is the preferred embodiment of the invention, as 20 described below.